A semiconductor device mounted within a carrier package has a maximum operating temperature dictated by the heat removal methods of the carrier package. If heat generated by a packaged semiconductor device is not effectively dissipated via the device's carrier package, the temperature of the device will increase until the device's maximum operating temperature is exceeded (i.e., until the device overheats), and the device will be damaged or destroyed.
Most semiconductor devices are formed from bulk silicon (e.g., from bulk silicon wafers), a material that has excellent thermal conduction properties. A bulk silicon device primarily dissipates heat through the backside of the silicon wafer die from which the silicon device is formed. For example, a conventional "packaged" semiconductor device may comprise a silicon wafer die having circuit elements formed on a first side or "frontside" thereof, an alumina substrate coupled to the frontside of the wafer die via a plurality of solder balls, a module cover coupled to a second or "backside" of the wafer die and to the substrate, and a heat sink coupled to the module cover. Heat primarily is dissipated from the semiconductor device via a "backside" thermal path from the frontside to the backside of the wafer die, from the backside of the wafer die to the module cover, from the module cover to the heat sink, and from the heat sink to the ambient environment.
Backside thermal paths are fairly effective at removing heat from semiconductor devices formed from bulk silicon wafers. However, the drive for higher speed and higher density circuits has lead to the use of non-conventional device materials such as silicon-on-insulator (SOI) wafers. An SOI wafer possesses an electrically insulating region between the frontside of the wafer (e.g., where the circuit elements are formed) and the backside of the wafer (e.g., where a module cover and a heat sink typically are coupled). This electrically insulating region has poor thermal conduction properties and significantly decreases the efficiency with which heat is conducted from the frontside to the backside of an SOI wafer (e.g., increases the "thermal resistance" of the wafer's backside thermal path). Therefore, conventional backside thermal paths are ineffective at removing heat from semiconductor devices formed on SOI wafers (i.e., SOI devices).
Accordingly, a need exists for a method and apparatus for removing heat from semiconductor devices formed on semiconductor wafers having backside thermal paths of high thermal resistance.